This invention relates generally to solid state light sources, and more particularly the invention relates to a step quantum well IR source which can be optically pumped.
Optoelectronic devices utilizing intersubband transitions for light emission are known. Typical are heterojunction or tunneling barrier structures. See Coon et al. U.S. Pat. No. 4,760,430, for example, in which a tunneling barrier is used. In the quantum well, electrons are pumped from one energy level to a higher energy level, and as the electrons return to the first energy level, light (photons) are emitted. In a three level laser device, the electrons are pumped up two energy levels, while in the four level laser device electrons are pumped up three energy levels. In both structures, a "population inversion" must exist between two energy levels for lasing or light emission to occur. The "population inversion" is a function of relaxation rate from one energy level to a lower level. Carriers (electrons or holes) must relax out of one energy level to lower level faster than carriers relax into the one energy level.
Coon et al., supra, disclose a tunneling barrier structure which uses current injection and tunneling for population inversion. The tunneling structure is defined by an AlGaAs layer and an undoped GaAs layer between two doped GaAs contact layers. A voltage potential is applied across the multi layer structure which enables the device to generate photon emission.
For a symmetric quantum well, the dipole matrix elements of transitions for odd-to-odd or even-to-even (e.g. 1 to 3 and 2 to 4) quantum numbers vanish, since the envelope functions of these energy states have the same parity due the symmetry of the well. The symmetry of a square quantum well can be broken by applying electric field, and then the normally forbidden transitions are allowed.